Which vessels carry the darker blood and how does the circulatory system work?

The circulatory system includes:

Fluid constantly circulates through two vicious circles. Small supplies the vascular tubes of the brain, neck, upper body. Large - vessels lower section body, legs. In addition, placental (available during fetal development) and coronary circles circulation.

The structure of the heart

The heart is a hollow cone made up of muscle tissue. In all people, the body is slightly different in shape, sometimes in structure. It has 4 sections - the right ventricle (RV), the left ventricle (LV), right atrium(PP) and the left atrium (LP), which communicate with each other through holes.

The holes are covered with valves. Between the left departments - mitral valve, between the right - tricuspid.

The pancreas pushes fluid into the pulmonary circulation - through the pulmonary valve to the pulmonary trunk. The LV has denser walls, as it pushes blood to the systemic circulation, through aortic valve, i.e. must create sufficient pressure.

After a portion of the liquid is ejected from the department, the valve is closed, which ensures the movement of the liquid in one direction.

Functions of the arteries

The arteries supply oxygenated blood. Through them, it is transported to all tissues and internal organs. The walls of the vessels are thick and highly elastic. Fluid is ejected into the artery under high pressure - 110 mm Hg. Art., and elasticity is a vital quality that keeps the vascular tubes intact.

The artery has three sheaths that ensure its ability to perform its functions. Middle shell consists of smooth muscle tissue, which allows the walls to change the lumen depending on body temperature, the needs of individual tissues or under high pressure. Penetrating into the tissues, the arteries narrow, passing into the capillaries.

Functions of capillaries

Capillaries penetrate all tissues of the body, except for the cornea and epidermis, carry oxygen to them and nutrients. The exchange is possible due to the very thin wall of the vessels. Their diameter does not exceed the thickness of the hair. Gradually, the arterial capillaries pass into the venous ones.

Functions of the veins

Veins carry blood to the heart. They are larger than arteries and contain about 70% of the total blood volume. Along the way venous system there are valves that work on the principle of the heart. They allow blood to pass through and close behind it to prevent its outflow. Veins are divided into superficial, located directly under the skin, and deep - passing in the muscles.

The main task of the veins is to transport blood to the heart, in which there is no longer oxygen and decay products are present. Only the pulmonary veins carry oxygenated blood to the heart. There is an upward movement. In case of violation of the normal operation of the valves, the blood stagnates in the vessels, stretching them and deforming the walls.

What are the reasons for the movement of blood in the vessels:

myocardial contraction;
contraction of the smooth muscle layer of blood vessels;
difference in blood pressure between arteries and veins.

The movement of blood through the vessels

Blood moves through the vessels continuously. Somewhere faster, somewhere slower, it depends on the diameter of the vessel and the pressure under which blood is ejected from the heart. The speed of movement through the capillaries is very low, due to which metabolic processes are possible.

The blood moves in a vortex, bringing oxygen along the entire diameter of the vessel wall. Due to such movements, oxygen bubbles seem to be pushed out of the boundaries of the vascular tube.

Blood healthy person flows in one direction, the outflow volume is always equal to the inflow volume. The reason for the continuous movement is due to the elasticity of the vascular tubes and the resistance that the fluid has to overcome. When blood enters, the aorta with the artery stretches, then narrows, gradually passing fluid further. Thus, it does not move in jerks, as the heart contracts.

Small circle of blood circulation

The small circle diagram is shown below. Where, RV - right ventricle, LS - pulmonary trunk, RLA - right pulmonary artery, LLA - left pulmonary artery, PG - pulmonary veins, LA - left atrium.

Through the pulmonary circulation, the fluid passes to the pulmonary capillaries, where it receives oxygen bubbles. The oxygenated fluid is called arterial. From the LP, it passes to the LV, where the bodily circulation originates.

Systemic circulation

Scheme of the corporal circle of blood circulation, where: 1. Left - left ventricle.

3. Art - arteries of the trunk and limbs.

5. PV - vena cava (right and left).

6. PP - right atrium.

The bodily circle is aimed at spreading a liquid full of oxygen bubbles throughout the body. It carries O 2 , nutrients to the tissues, collecting decay products and CO 2 along the way. After that, there is a movement along the route: PZH - LP. And then it starts again through the pulmonary circulation.

Personal circulation of the heart

The heart is an "autonomous republic" of the body. It has its own system of innervation, which sets the muscles of the organ in motion. And its own circle of blood circulation, which is made up of coronary arteries with veins. The coronary arteries independently regulate the blood supply to the heart tissues, which is important for the continuous functioning of the organ.

The structure of the vascular tubes is not identical. Most people have two coronary arteries, but there is a third. The heart can be fed from the right or left coronary artery. Because of this, it is difficult to establish the norms of cardiac circulation. The intensity of blood flow depends on the load, physical training, the age of the person.

Placental circulation

Placental circulation is inherent in every person at the stage of fetal development. The fetus receives blood from the mother through the placenta, which forms after conception. From the placenta, it moves to the umbilical vein of the child, from where it goes to the liver. This explains the large size of the latter.

The arterial fluid enters the vena cava, where it mixes with the venous fluid, then goes to the left atrium. From it, blood flows to the left ventricle through a special hole, after which it goes directly to the aorta.

The movement of blood in the human body in a small circle begins only after birth. With the first breath, the vessels of the lungs expand, and they develop for a couple of days. oval hole in the heart can persist for a year.

Circulatory pathologies

Blood circulation is carried out in a closed system. Changes and pathologies in the capillaries can adversely affect the functioning of the heart. Gradually, the problem will worsen and develop into a serious disease. Factors affecting the movement of blood:

Pathologies of the heart and large vessels lead to the fact that the blood flows to the periphery in insufficient volume. Toxins stagnate in the tissues, they do not receive proper oxygen supply and gradually begin to break down.
Blood pathologies such as thrombosis, stasis, embolism lead to blockage of blood vessels. Movement through the arteries and veins becomes difficult, which deforms the walls of blood vessels and slows down the flow of blood.
vascular deformity. The walls can become thinner, stretch, change their permeability and lose elasticity.
Hormonal pathologies. Hormones are able to increase blood flow, which leads to strong filling vessels.
Compression of blood vessels. When the blood vessels are compressed, the blood supply to the tissues stops, which leads to cell death.
Violations of the innervation of organs and injuries can lead to the destruction of the walls of arterioles and provoke bleeding. Also, a violation of normal innervation leads to a disorder of the entire circulatory system.
Infectious diseases of the heart. For example, endocarditis, in which the valves of the heart are affected. The valves do not close tightly, which contributes to the backflow of blood.
Damage to the vessels of the brain.
Diseases of the veins in which the valves are affected.

Also, the way of life of a person affects the movement of blood. Athletes have a more stable circulatory system, so they are more enduring and even fast running will not immediately speed up the heart rate.

The average person can undergo changes in blood circulation even from smoking a cigarette. With injuries and ruptures of blood vessels circulatory system is able to create new anastomoses to provide blood to the "lost" areas.

Regulation of blood circulation

Any process in the body is controlled. There is also regulation of blood circulation. The activity of the heart is activated by two pairs of nerves - sympathetic and vagus. The first excite the heart, the second slow down, as if controlling each other. severe irritation vagus nerve can stop the heart.

A change in the diameter of the vessels also occurs due to nerve impulses from the medulla oblongata. The heart rate increases or decreases depending on signals received from external irritation, such as pain, temperature changes, etc.

In addition, the regulation of cardiac work occurs due to substances contained in the blood. For example, adrenaline increases the frequency of myocardial contractions and at the same time constricts blood vessels. Acetylcholine has the opposite effect.

All these mechanisms are needed to maintain constant uninterrupted work in the body, regardless of changes in the external environment.

The cardiovascular system

The above is only a brief description of the human circulatory system. The body contains a huge number of blood vessels. The movement of blood in a large circle passes through the entire body, providing blood to every organ.

The cardiovascular system also includes organs lymphatic system. This mechanism works in concert, under the control of neuro-reflex regulation. The type of movement in the vessels can be direct, which excludes the possibility of metabolic processes, or vortex.

The movement of blood depends on the work of each system in the human body and cannot be described by a constant value. It varies depending on the set of external and internal factors. For different organisms existing in different conditions, have their own norms of blood circulation, under which normal life will not be in danger.

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What vessels carry blood away from the heart

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Circulation is the continuous movement of blood through a closed cardiovascular system, which ensures the exchange of gases in the lungs and body tissues.

In addition to providing tissues and organs with oxygen and removing carbon dioxide from them, blood circulation delivers nutrients, water, salts, vitamins, hormones to cells and removes metabolic end products, and also maintains a constant body temperature, ensures humoral regulation and the interconnection of organs and organ systems in body.

The circulatory system consists of the heart and blood vessels that permeate all organs and tissues of the body.

Blood circulation begins in the tissues, where metabolism takes place through the walls of the capillaries. The blood that has given oxygen to organs and tissues enters the right half of the heart and is sent to the pulmonary (pulmonary) circulation, where the blood is saturated with oxygen, returns to the heart, entering its left half, and again spreads throughout the body (large circulation) .

The heart is the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), separated by an interatrial septum, and two ventricles (right and left), separated interventricular septum. The right atrium communicates with the right ventricle through the tricuspid ventricle, and the left atrium communicates with the left ventricle through butterfly valve. The mass of the heart of an adult is on average about 250 g in women and about 330 g in men. The length of the heart is cm, the transverse size is 8-11 cm and the anteroposterior is 6-8.5 cm. The volume of the heart in men is on average cm 3, and in women cm 3.

The outer walls of the heart are formed by the cardiac muscle, which is similar in structure to the striated muscles. However, the heart muscle is distinguished by the ability to automatically contract rhythmically due to impulses that occur in the heart itself, regardless of external influences(automatic heart).

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart contracts about once per minute at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

atrial contraction - atrial systole - takes 0.1 s
ventricular contraction - ventricular systole - takes 0.3 s
total pause - diastole (simultaneous relaxation of the atria and ventricles) - takes 0.4 s

Thus, during the entire cycle, the atria work 0.1 s and rest 0.7 s, the ventricles work 0.3 s and rest 0.5 s. This explains the ability of the heart muscle to work without fatigue throughout life. The high efficiency of the heart muscle is due to the increased blood supply to the heart. Approximately 10% of the blood ejected from the left ventricle into the aorta enters the arteries departing from it, which feed the heart.

Arteries are blood vessels that carry oxygenated blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).

The wall of the artery is represented by three layers: the outer connective tissue membrane; middle, consisting of elastic fibers and smooth muscles; internal, formed by the endothelium and connective tissue.

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total volume of blood in arterial system averages 950 ml. Arteries gradually branch into smaller and smaller vessels - arterioles, which pass into capillaries.

Capillaries (from the Latin “capillus” - hair) are the smallest vessels (the average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans that have a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of the capillaries, consisting of endothelial cells, there is an exchange of gases and other substances between the blood and various tissues.

Veins are blood vessels that carry blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (with the exception of pulmonary veins that carry arterial blood). The wall of the vein is much thinner and more elastic than the wall of the artery. Small and medium-sized veins are equipped with valves that prevent the reverse flow of blood in these vessels. In humans, the volume of blood in the venous system averages 3200 ml.

The movement of blood through the vessels was first described in 1628. English doctor V. Harvey.

Harvey William () - English physician and naturalist. He created and introduced into the practice of scientific research the first experimental method - vivisection (live cutting).

In 1628 he published the book "Anatomical Studies on the Movement of the Heart and Blood in Animals", in which he described the large and small circles of blood circulation, formulated the basic principles of blood movement. The date of publication of this work is considered the year of the birth of physiology as an independent science.

In humans and mammals, blood moves through a closed cardiovascular system, consisting of a large and small circles of blood circulation (Fig.).

A large circle starts from the left ventricle, carries blood through the aorta throughout the body, gives oxygen to the tissues in the capillaries, takes carbon dioxide, turns from arterial to venous and returns to the right atrium through the superior and inferior vena cava.

The pulmonary circulation starts from the right ventricle, carries blood through the pulmonary artery to the pulmonary capillaries. Here the blood gives off carbon dioxide, is saturated with oxygen and flows through the pulmonary veins to the left atrium. From the left atrium through the left ventricle, blood again enters the systemic circulation.

Small circle of blood circulation- pulmonary circle - serves to enrich the blood with oxygen in the lungs. It starts from the right ventricle and ends at the left atrium.

From the right ventricle of the heart, venous blood enters the pulmonary trunk (common pulmonary artery), which soon divides into two branches that carry blood to the right and left lungs.

In the lungs, arteries branch into capillaries. In the capillary networks braiding the pulmonary vesicles, the blood gives off carbon dioxide and receives a new supply of oxygen in return (pulmonary respiration). Oxygenated blood acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, having merged into four pulmonary veins (two on each side), flow into the left atrium of the heart. In the left atrium, the small (pulmonary) circle of blood circulation ends, and the blood that enters the atrium arterial blood passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

Systemic circulation- bodily - collects venous blood from the upper and lower half of the body and similarly distributes arterial blood; starts from the left ventricle and ends with the right atrium.

From the left ventricle of the heart, blood enters the largest arterial vessel - the aorta. Arterial blood contains nutrients and oxygen necessary for the life of the body and has a bright scarlet color.

The aorta branches into arteries that go to all organs and tissues of the body and pass in their thickness into arterioles and further into capillaries. Capillaries, in turn, are collected in venules and further into veins. Through the wall of the capillaries there is a metabolism and gas exchange between the blood and body tissues. Arterial blood flowing in the capillaries gives off nutrients and oxygen and in return receives metabolic products and carbon dioxide (tissue respiration). As a result, the blood entering the venous bed is poor in oxygen and rich in carbon dioxide and therefore has a dark color - venous blood; when bleeding, the color of the blood can determine which vessel is damaged - an artery or a vein. The veins merge into two large trunks - the superior and inferior vena cava, which flow into the right atrium of the heart. This part of the heart ends with a large (corporeal) circle of blood circulation.

In the systemic circulation, arterial blood flows through the arteries, and venous blood flows through the veins.

In a small circle, on the contrary, venous blood flows from the heart through the arteries, and arterial blood returns to the heart through the veins.

The addition to the great circle is third (cardiac) circulation serving the heart itself. It begins with the coronary arteries of the heart emerging from the aorta and ends with the veins of the heart. The latter merge into the coronary sinus, which flows into the right atrium, and the remaining veins open directly into the atrial cavity.

The movement of blood through the vessels

Any fluid flows from a place where the pressure is higher to where it is lower. The greater the pressure difference, the higher the flow rate. The blood in the vessels of the systemic and pulmonary circulation also moves due to the pressure difference that the heart creates with its contractions.

In the left ventricle and aorta, blood pressure is higher than in the vena cava (negative pressure) and in the right atrium. The pressure difference in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low in the pulmonary veins and left atrium ensure the movement of blood in the pulmonary circulation.

The highest pressure is in the aorta and large arteries (blood pressure). Arterial blood pressure is not a constant value [show]

Blood pressure- this is the pressure of blood on the walls of blood vessels and chambers of the heart, resulting from the contraction of the heart, pumping blood into vascular system, and vascular resistance. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries - blood pressure.

Arterial blood pressure is not a constant value. In healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the pressure level in the arteries during the systole of the heart is about 120 mm Hg, and the minimum, or diastolic - the pressure level in the arteries during the diastole of the heart is about 80 mm Hg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the time of systole, it rises to damm Hg. Art., and during diastole decreases domm Hg. Art. These pulse pressure oscillations occur simultaneously with the pulse oscillations of the arterial wall.

Pulse- periodic jerky expansion of the walls of the arteries, synchronous with the contraction of the heart. The pulse is used to determine the number of heartbeats per minute. In an adult, the average heart rate is beats per minute. At physical activity the pulse rate may increase until the beats. In places where the arteries are located on the bone and lie directly under the skin (radial, temporal), the pulse is easily felt. The propagation speed of the pulse wave is about 10 m/s.

By the amount blood pressure affect:

work of the heart and force of cardiac contraction;
the size of the lumen of the vessels and the tone of their walls;
the amount of blood circulating in the vessels;
blood viscosity.

A person's blood pressure is measured in the brachial artery, comparing it with atmospheric pressure. For this, a rubber cuff connected to a pressure gauge is put on the shoulder. The cuff is inflated with air until the pulse at the wrist disappears. This means that the brachial artery is compressed by a lot of pressure, and blood does not flow through it. Then, gradually releasing air from the cuff, monitor the appearance of a pulse. At this moment, the pressure in the artery becomes slightly higher than the pressure in the cuff, and the blood, and with it the pulse wave begin to reach the wrist. The readings of the pressure gauge at this time characterize the blood pressure in the brachial artery.

A persistent increase in blood pressure above the indicated figures at rest is called hypertension, and its decrease is called hypotension.

Blood pressure is regulated by the nervous and humoral factors(see table).

(diastolic)

The speed of blood movement depends not only on the pressure difference, but also on the width of the bloodstream. Although the aorta is the widest vessel, it is the only one in the body and all the blood flows through it, which is pushed out by the left ventricle. Therefore, the speed here is maximum mm/s (see Table 1). As the arteries branch out, their diameter decreases, but the total cross-sectional area of all arteries increases and the blood velocity decreases, reaching 0.5 mm/s in the capillaries. Due to such a low rate of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and take their waste products.

The slowing down of blood flow in the capillaries is explained by their huge amount(about 40 billion) and a large total lumen (800 times the lumen of the aorta). The movement of blood in the capillaries is carried out by changing the lumen of the supply small arteries: their expansion increases the blood flow in the capillaries, and their narrowing decreases it.

The veins on the way from the capillaries, as they approach the heart, enlarge, merge, their number and total lumen bloodstream decreases, and the speed of blood movement in comparison with the capillaries increases. From Table. 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins can easily stretch, so they can contain significantly more blood than the corresponding arteries.

The main reason for the movement of blood through the veins is the pressure difference at the beginning and end of the venous system, so the movement of blood through the veins occurs in the direction of the heart. This is facilitated by the suction action chest("respiratory pump") and abbreviation skeletal muscles("muscle pump"). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and at the end of the venous system increases, and the blood through the veins is sent to the heart. Skeletal muscles, contracting, compress the veins, which also contributes to the movement of blood to the heart.

The relationship between the speed of blood flow, the width of the bloodstream and blood pressure is illustrated in Fig. 3. The amount of blood flowing per unit of time through the vessels is equal to the product of the speed of blood movement by the cross-sectional area of the vessels. This value is the same for all parts of the circulatory system: how much blood pushes the heart into the aorta, how much it flows through the arteries, capillaries and veins, and the same amount returns back to the heart, and is equal to the minute volume of blood.

Redistribution of blood in the body

If the artery extending from the aorta to any organ, due to the relaxation of its smooth muscles, expands, then the organ will receive more blood. At the same time, other organs will receive less blood due to this. This is how blood is redistributed in the body. As a result of redistribution, more blood flows to the working organs at the expense of the organs that are currently at rest.

The redistribution of blood is regulated by the nervous system: simultaneously with the expansion of blood vessels in the working organs, the blood vessels of the non-working organs narrow and blood pressure remains unchanged. But if all the arteries dilate, this will lead to a drop in blood pressure and to a decrease in the speed of blood movement in the vessels.

Blood circulation time

Circulation time is the time it takes for blood to travel through the entire circulation. A number of methods are used to measure blood circulation time. [show]

The principle of measuring the time of the blood circulation is that some substance that is not usually found in the body is injected into the vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes an action characteristic of it. For example, in cubital vein inject a solution of the alkaloid lobeline, which acts through the blood on the respiratory center of the medulla oblongata, and determine the time from the moment the substance is injected until the moment when a short-term breath holding or cough appears. This happens when the lobelin molecules, having made a circuit in the circulatory system, act on the respiratory center and cause a change in breathing or coughing.

AT last years the rate of blood circulation in both circles of blood circulation (or only in a small, or only in a large circle) is determined using a radioactive isotope of sodium and an electron counter. To do this, several of these counters are placed on different parts bodies near large vessels and in the region of the heart. After the introduction of a radioactive isotope of sodium into the cubital vein, the time of appearance of radioactive radiation in the region of the heart and studied vessels.

The circulation time of the blood in humans is on average about 27 systoles of the heart. With heartbeats per minute, the complete circulation of blood occurs in about a second. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than that of its walls, and also that not all vascular regions have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

Studies on dogs have shown that 1/5 of the time of a complete blood circulation occurs in the pulmonary circulation and 4/5 in the systemic circulation.

Innervation of the heart. The heart, like other internal organs, is innervated by the autonomic nervous system and receives dual innervation. Sympathetic nerves approach the heart, which strengthen and accelerate its contractions. The second group of nerves - parasympathetic - acts on the heart in the opposite way: it slows down and weakens heart contractions. These nerves regulate the heart.

In addition, the work of the heart is affected by the hormone of the adrenal glands - adrenaline, which enters the heart with blood and increases its contractions. The regulation of the work of organs with the help of substances carried by the blood is called humoral.

Nervous and humoral regulation of the heart in the body act in concert and provide an accurate adaptation of the activity of the cardiovascular system to the needs of the body and environmental conditions.

Innervation of blood vessels. Blood vessels are innervated by sympathetic nerves. Excitation propagating through them causes contraction of smooth muscles in the walls of blood vessels and constricts blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will expand. Therefore, along the sympathetic nerves to blood vessels all the time there is an excitation that keeps these vessels in a state of some narrowing - vascular tone. When excitation increases, the frequency of nerve impulses increases and the vessels narrow more strongly - vascular tone increases. On the contrary, with a decrease in the frequency of nerve impulses due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. To the vessels of some organs (skeletal muscles, salivary glands) in addition to vasoconstrictor, vasodilating nerves are also suitable. These nerves become excited and dilate the blood vessels of the organs as they work. Substances that are carried by the blood also affect the lumen of the vessels. Adrenaline constricts blood vessels. Another substance - acetylcholine - secreted by the endings of some nerves, expands them.

Regulation of the activity of the cardiovascular system. The blood supply of the organs varies depending on their needs due to the described redistribution of blood. But this redistribution can only be effective if the pressure in the arteries does not change. One of the main functions nervous regulation circulation is to maintain a constant blood pressure. This function is carried out reflexively.

in the wall of the aorta and carotid arteries there are receptors that are more irritated if blood pressure exceeds normal levels. Excitation from these receptors goes to the vasomotor center located in the medulla oblongata and inhibits its work. From the center along the sympathetic nerves to the vessels and the heart, a weaker excitation begins to flow than before, and the blood vessels dilate, and the heart weakens its work. As a result of these changes, blood pressure decreases. And if for some reason the pressure falls below the norm, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, intensifies its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels constrict, the heart contracts, more often and stronger, blood pressure rises.

Hygiene of cardiac activity

The normal activity of the human body is possible only in the presence of a well-developed cardiovascular system. The rate of blood flow will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. At physical work the need of organs for oxygen increases simultaneously with the intensification and acceleration of heart contractions. Only a strong heart muscle can provide such work. To be resilient to a variety of labor activity, it is important to train the heart, increase the strength of its muscles.

Physical labor, physical education develop the heart muscle. To provide normal function cardiovascular system, a person should start his day with morning exercises, especially people whose professions are not related to physical labor. To enrich the blood with oxygen physical exercises best done outdoors.

It must be remembered that excessive physical and mental stress can cause disruption of the normal functioning of the heart, its diseases. Especially bad influence alcohol, nicotine, and drugs affect the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing sharp disturbances in the regulation of vascular tone and heart activity. They lead to the development of severe diseases of the cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to develop spasms of the heart vessels, causing severe heart attacks and sometimes death.

First aid for wounds and bleeding

Injuries are often accompanied by bleeding. There are capillary, venous and arterial bleeding.

Capillary bleeding occurs even with a minor injury and is accompanied by a slow flow of blood from the wound. Such a wound should be treated with a solution of brilliant green (brilliant green) for disinfection and a clean gauze bandage should be applied. The bandage stops bleeding, promotes the formation of a blood clot and prevents microbes from entering the wound.

Venous bleeding is characterized by a significantly higher rate of blood flow. The flowing blood is dark color. To stop bleeding, it is necessary to apply a tight bandage below the wound, that is, further from the heart. After the bleeding has stopped, the wound is treated disinfectant (3% peroxide solution hydrogen, vodka), bandage with a sterile pressure bandage.

With arterial bleeding, scarlet blood gushes from the wound. This is the most dangerous bleeding. If the artery of the limb is damaged, it is necessary to raise the limb as high as possible, bend it and press the wounded artery with your finger in the place where it comes close to the surface of the body. It is also necessary to apply a rubber tourniquet above the wound site, i.e. closer to the heart (you can use a bandage, a rope for this) and tighten it tightly to completely stop the bleeding. The tourniquet must not be kept tightened for more than 2 hours. When it is applied, a note must be attached in which the time of applying the tourniquet should be indicated.

It should be remembered that venous, and even more arterial bleeding can lead to significant blood loss and even death. Therefore, when injured, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Strong pain or fright can cause the person to lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient supply of blood to the brain. The unconscious person should be allowed to smell some non-toxic strong smell substance (eg. ammonia), moisten the face with cold water or lightly pat it on the cheeks. When olfactory or skin receptors are stimulated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives sufficient nutrition, and consciousness returns.

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The constant movement of blood through a closed cardiovascular system, which provides gas exchange in tissues and lungs, is called blood circulation. In addition to saturating the organs with oxygen, as well as cleansing them of carbon dioxide, blood circulation is responsible for delivering all the necessary substances to the cells.

Everyone knows that blood is venous and arterial. In this article, you will learn which vessels move more dark blood, find out what is included in this biological fluid.

This system includes blood vessels that permeate all tissues of the body and the heart. The process of blood circulation in the tissues begins, where metabolic processes occur through the capillary walls.

The blood, which has given away all the useful substances, flows first to the right half of the heart, and then to the pulmonary circulation. There, it, enriched with useful substances, moves to the left, and then spreads in a large circle.

The heart is the main organ in this system.. It is endowed with four chambers - two atria and two ventricles. The atria are separated by the atrial septum, and the ventricles by the interventricular septum. The weight of the human "motor" is from 250-330 grams.

The color of blood in the veins and the color of blood moving through the arteries are slightly different. About which vessels darker blood moves, and why it differs in shade, you will learn a little later.

An artery is a vessel that carries biological fluid saturated with useful substances from the "motor" to the organs. The answer to a fairly frequently asked question: "Which vessels carry venous blood?" simple. Deoxygenated blood transported exclusively by the pulmonary artery.

The arterial wall consists of several layers, these include:

outer connective tissue sheath;
middle (it is made up of smooth muscles and elastic hairs);
internal (consisting of connective tissue and endothelium).

Arteries divide into small vessels called arterioles. As for the capillaries, they are the smallest vessels.

The vessel that carries carbon dioxide-enriched blood from the tissues to the heart is called a vein. Exception in this case pulmonary vein - as it carries arterial blood.

For the first time, Dr. V. Harvey wrote about blood circulation back in 1628. The circulation of biological fluid occurs through the small and large circles of blood circulation.

The movement of biological fluid in a large circle starts from the left ventricle, thanks to high blood pressure, blood spreads throughout the body, nourishes all organs with useful substances and takes away harmful ones. Further, the transformation of arterial blood into venous blood is noted. Final stage return of blood to the right atrium.

As for the small circle, it starts from the right ventricle. First, the blood gives off carbon dioxide, receives oxygen, and then moves to the left atrium. Further, through the right ventricle, the flow of biological fluid into the large circle is noted.

The question of which vessels carry the darker blood is quite common. Blood has a red color, it differs only in shades due to the amount of hemoglobin and oxygen enrichment.

Surely, many people remember from biology lessons that arterial blood has a scarlet tint, and venous blood has a dark red or burgundy tint. Veins located near the skin are also red when blood circulates through them.

In addition, venous blood differs not only in color, but in function. Now, knowing which vessels the darker blood moves through, you know that its color is due to its enrichment with carbon dioxide. The blood in the veins has a burgundy hue.

It has little oxygen, but at the same time it is rich in metabolic products. She is more viscous. This is due to an increase in the diameter of red blood cells due to the intake of carbon dioxide into them. In addition, the temperature of the venous blood is higher, and the pH is lower.

It circulates through the veins very slowly (due to the presence of valves in the veins that slow down the speed of its movement). Wen in human body compared to arteries, much more.

What color is the blood in the veins, and what functions does it perform

What color is the blood in the veins you know. The hue of the biological fluid determines the presence in the red blood cells(erythrocytes) hemoglobin. The blood circulating through the arteries, as already mentioned, is scarlet.

This is due to the high concentration of hemoglobin in it (in humans) and hemocyanin (in arthropods and mollusks), enriched with various nutrients.

Venous blood has a dark red tint. This is due to oxidized and reduced hemoglobin.

It is at least unreasonable to believe in the theory that the biological fluid circulating through the vessels is bluish in color, and when injured and in contact with air due to chemical reaction blushes immediately. It is a myth.

The veins can only appear bluish, this is due to the simple laws of physics.. When light hits the body, the skin beats off part of all the waves and therefore looks light, well, or dark (depending on the concentration of the coloring pigment).

What color is venous blood, you know, now let's talk about the composition. It is possible to distinguish arterial blood from venous blood using laboratory tests. Oxygen tension - 38-40 mm Hg. (in the venous), and in the arterial - 90. The content of carbon dioxide in the venous blood is 60 millimeters of mercury, and in the arterial - about 30. The pH level in the venous blood is 7.35, and in the arterial - 7.4.

The outflow of blood, which carries away carbon dioxide and metabolic products, is carried out through the veins. It is enriched with useful substances that are absorbed into the walls of the gastrointestinal tract and produced by ZhVS.

Now you know what color the blood is in the veins, you are familiar with its composition and functions.

The blood flowing through the veins overcomes "difficulties" during movement, which include pressure and gravity. That is why, in case of damage, the biological fluid flows in a slow stream. But in the event of an injury to the arteries, blood spurts out in a fountain.

The speed at which venous blood moves is much less than the speed at which arterial blood moves. The heart pumps out blood at high pressure. After passing through the capillaries and turning into a venous, there is a decrease in pressure to ten millimeters of mercury.

Why venous blood is darker than arterial blood, and how to determine the type of bleeding

You already know why venous blood is darker than arterial blood. Arterial blood is lighter and this is due to the presence of oxyhemoglobin in it. As for the venous, it is dark (due to the content of both oxidized and reduced hemoglobin).

You probably noticed that blood is taken from a vein for analysis, and you probably wondered, “why from a vein?”. This is due to the following. The composition of venous blood includes substances that are formed during metabolism. In pathologies, it is enriched with substances that ideally should not be in the body. Due to their presence, a pathological process can be detected.

Now you know not only why the blood in the veins is darker than the arterial blood, but also why the blood is taken from the vein.

Everyone can determine the type of bleeding, there is nothing complicated about it. The main thing is to know the characteristics of the biological fluid. Venous blood has a darker hue (why venous blood is darker than arterial blood is mentioned above), and it is also much thicker. When cut, it flows out in a slow stream or drops. But as for the arterial, it is liquid and bright. When wounded, she sprays with a fountain.

Stop venous bleeding easier, sometimes it just stops. As a rule, a tight bandage (it is applied below the wound) is used to stop the bleeding.

As for arterial bleeding, then everything is much more complicated. It is dangerous because it does not stop on its own. In addition, blood loss can be so massive that literally in an hour death can occur.

Capillary bleeding can open even with minimal injury. The blood flows out calmly, in a small trickle. Such damage is treated with green paint. Then a bandage is applied to them, which helps to stop bleeding and prevent contact with pathogenic microorganisms into the wound.

As for the venous, when damaged, the blood flows out somewhat faster. In order to stop bleeding, a tight bandage is applied, as already mentioned, below the wound, that is, further from the heart. Next, the wound is treated with 3% peroxide or vodka and bandaged.

With regards to arterial, it is the most dangerous. If an injury has already happened and you see that bleeding from an artery, you must immediately raise the limb as high as possible. Next, you need to bend it, pinch the wounded artery with your finger.

Then a rubber tourniquet is applied (a rope or bandage will do) above the wound, after which it is tightly tightened. The tourniquet must be removed no later than two hours after application. At the time of applying the bandage, a note is attached that indicates the time the tourniquet was applied.

Bleeding is dangerous and fraught severe loss blood and even lethal outcome. That is why in case of injury it is necessary to call ambulance or take the patient to the hospital.

Now you know why the blood in the veins is darker than arterial. The blood circulation is a closed system, which is why the blood in it is either arterial or venous.

Venous circulation occurs as a result of the circulation of blood towards the heart, and in general, through the veins. It is deprived of oxygen, as it is completely dependent on carbon dioxide, which is necessary for tissue gas exchange.

As for human venous blood, in contrast to arterial, then it is several times warmer and has a lower pH. In its composition, doctors note the low content of most nutrients, including glucose. It is characterized by the presence of metabolic end products.

In order to receive venous blood, you must undergo a procedure called venipuncture! Basically everything medical research in laboratory conditions, it is venous blood that is taken as the basis. Unlike arterial, it has a characteristic color with a red-bluish, deep tint.

About 300 years ago the explorer Van Horn made a sensational discovery: it turns out that the entire human body is permeated by capillaries! The doctor begins to make various experiments with medicines, as a result he observes the behavior of capillaries filled with red liquid. Modern doctors know that capillaries play a key role in the human body. With their help, blood flow is gradually provided. Thanks to them, oxygen is supplied to all organs and tissues.

Human arterial and venous blood, difference

From time to time, one asks the question: is venous blood different from arterial blood? The entire human body is divided into numerous veins, arteries, large and small vessels. Arteries contribute to the so-called outflow of blood from the heart. Purified blood moves throughout the human body and thus provides timely nutrition.

In this system, the heart is a kind of pump that gradually distills blood throughout the body. Arteries can be located both deep and close under the skin. You can feel the pulse not only on the wrist, but also on the neck! Arterial blood has a characteristic bright red hue, which, when bleeding, acquires a somewhat poisonous color.

Human venous blood, unlike arterial blood, is located very close to the surface of the skin. On the entire surface of its length, venous blood is accompanied by special valves that contribute to a calm and even passage of blood. Dark blue blood nourishes the tissues and gradually moves into the veins.

In the human body, there are several times more veins than arteries. In case of any damage, venous blood flows slowly and stops very quickly. Venous blood is very different from arterial blood, and all because of the structure of individual veins and arteries.

The walls of the veins are unusually thin, unlike the arteries. They can withstand high pressure, as powerful shocks can be observed during the ejection of blood from the heart.

In addition, elasticity plays a key role, due to which the movement of blood through the vessels occurs quickly. Veins and arteries provide normal blood circulation, which does not stop even for a minute in the human body. Even if you are not a doctor, it is very important to know a minimum of information about venous and arterial blood that will help you quickly provide first aid in case of open bleeding. The World Wide Web will help to replenish the stock of knowledge regarding venous and arterial circulation. You just need to enter the word of interest in the search box and in a few minutes you will receive answers to all your questions.

This video shows the process of converting arterial blood into venous blood:

Venous blood flows in the pulmonary artery. Arteries are called vessels that go from the heart, and veins - going to the heart.

There are two circulations in the human body. From the left ventricle of the heart, arterial blood is pushed into a large circle and spreads throughout the body, through ever smaller vessels - to each cell, giving oxygen and nutrients to cells and tissues and taking away unnecessary metabolic products.

After that, venous blood, through increasingly larger vessels, rises to the right atrium, and is pushed out of the right ventricle of the heart into the pulmonary circulation through the pulmonary artery.

In the lungs, the blood is enriched with oxygen and gives off volatile metabolic products that leave the body with exhaled air. Further, the blood through the pulmonary vein enters the left atrium - into the left ventricle and through the aorta again into the systemic circulation.

So, do we know how the human body works? You ask: "Why do you need to know?"

If you have a car and you do not know how it works, you will have to turn to a specialist for the slightest malfunction. Often the situation will look something like this:

“Vasily was going to go with his family to nature on the weekend, but the car would not start. The weekend is gone! The family is at a loss ... Then Vasily notices Ivan, who is busy in the yard with his car and asks him for help.

Ivan inspects the car and says that he can help quickly and the repair will cost 500 rubles. Vasily happily agrees, gives the money, after which the neighbor twists two wires together and the problem is solved.

Vasily is indignant that he paid as much as 200 rubles for such a trifle, and Ivan objects that he took the money not for what he did, but because he KNEW what needed to be done.

Now consider a situation where a person injured his leg, and a very heavy bleeding. How to stop the bleeding, prevent life-threatening blood loss? You will say that it is simple - you need to apply a tourniquet. Right. And the sooner you do it, the better.

But do YOU know where to take the tourniquet, where and how to apply it? The tourniquet can be made from a scarf, scarf or tie, you can tear off the sleeve from the shirt, tear off the T-shirt. This is easy to figure out.

Where to put it? Above or below the bleeding site?

Arterial blood flows from top to bottom, it is scarlet in color and spurts when bleeding. A tourniquet for arterial bleeding should be applied above the site of bleeding and tightened so that it stops.

Venous blood in the legs flows from the bottom up, it is dark, flows slowly. In this case, the tourniquet must be applied below the site of bleeding.
In any case, it is MANDATORY to note the time of applying the tourniquet. Write a note and stick it under the tourniquet, write the time with a pen on the leg or arm of the victim, remember it in the memory of the mobile phone.

Why should this be done? The tourniquet blocks the flow of blood to the leg, toxic metabolic products accumulate in the tissues and cannot be released. If the tourniquet has been tightened for more than two hours, it cannot be removed abruptly - self-poisoning may occur. In such a situation, the tourniquet is loosened slowly, gradually.

If you know the structure of the body well, you can not apply a tourniquet, but press the vessel with your finger: the artery is above the place of bleeding, the vein is below, and so wait for the ambulance to arrive. Then the blood to the tissues of the leg will flow through the bypass vessels and self-poisoning will not occur.

For the normal operation of all organs and systems of the human body, it is vital to constantly supply them with nutrients and oxygen, as well as the timely removal of decay products and waste products. Implementation of these critical processes ensured by constant blood circulation. In this article, we will look at the human circulatory system, and also tell you how blood from the arteries enters the veins, how it circulates through the blood vessels, and how the main organ of the circulatory system, the heart, works.

The study of blood circulation from antiquity to the 17th century

Human circulation has been of interest to many scientists for centuries. Even the ancient researchers, Hippocrates and Aristotle, assumed that all organs are somehow interconnected. They believed that the human circulation consists of two separate systems that are not connected to each other in any way. Of course, their ideas were wrong. They were refuted by the Roman physician Claudius Galen, who proved experimentally that the blood moves through the heart not only through the veins, but also through the arteries. Until the 17th century, scientists were of the opinion that blood enters from the right to the left atrium through the septum. It was only in 1628 that a breakthrough was made: the English anatomist William Harvey, in his Anatomical Study of the Movement of the Heart and Blood in Animals, presented his new theory of blood circulation. He experimentally proved that it moves through the arteries from the ventricles of the heart, and then returns through the veins to the atria and cannot be endlessly produced in the liver. was the first to quantify cardiac output. Based on his work, a modern scheme human circulation, comprising two circles.

Further studies of the circulatory system

For a long time remained unexplained important question: "How blood from the arteries gets into the veins." Only at the end of the 17th century, Marcello Malpighi discovered special links of blood vessels - capillaries that connect veins and arteries.

In the future, many scientists (Stephen Hales, Daniel Bernoulli, Euler, Poiseuille, and others) worked on the problem of blood circulation, including measuring venous and arterial blood pressure, volume, elasticity of arteries, and other parameters. In 1843, the scientist Jan Purkyne proposed scientific community hypothesis that the systolic decrease in the volume of the heart has a suction effect on the anterior edge of the left lung. In 1904, IP Pavlov made an important contribution to science by proving that there are four pumps in the heart, and not two, as previously thought. At the end of the twentieth century, it was possible to prove why the pressure in the cardiovascular system is higher than atmospheric pressure.

Physiology of circulation: veins, capillaries and arteries

Thanks to all scientific research, we now know that blood is constantly moving through special hollow tubes that have different diameters. They are not interrupted and pass into others, thereby forming a single closed circulatory system. In total, three types of vessels are known: arteries, veins, capillaries. All of them are different in structure. Arteries are vessels that carry blood away from the heart to organs. Inside they are lined with a single-layer epithelium, and outside they have a connective tissue membrane. The middle layer of the arterial wall is made up of smooth muscle.

by the most large vessel is the aorta. In organs and tissues, arteries divide into smaller vessels called arterioles. They, in turn, branch into capillaries, which consist of a single layer epithelial tissue and are located in the spaces between cells. Capillaries have special pores through which water, oxygen, glucose and other substances are transported into the tissue fluid. How does blood get from arteries to veins? From the organs, it goes, deprived of oxygen and enriched with carbon dioxide, and is sent through the capillaries to the venules. Then it returns to the right atrium through the inferior, superior vena cava and coronary veins. The veins are located more superficially and have special facilitating blood flow.

Circles of blood circulation

All vessels, uniting, form two circles, which are called large and small. The first ensures the saturation of the organs and tissues of the body with oxygen-rich blood. The systemic circulation is as follows: the left atrium simultaneously with the right is reduced, thereby ensuring the flow of blood into the left ventricle. From there, the blood is sent to the aorta, from which it continues to move through other arteries and arterioles, going in different directions to the tissues of the whole body. Then the blood returns through the veins and goes to the right atrium.

Blood and circulation: lesser circle

The second circle of blood circulation starts in the right ventricle and ends in the left atrium. It circulates blood through the lungs. The physiology of blood circulation in the small circle is as follows. Contraction of the right ventricle directs blood to the pulmonary trunk, which branches into the extensive network of pulmonary capillaries. The blood entering them is saturated with oxygen through ventilation of the lungs, after which it returns to the left atrium. It can be concluded that two circles of blood circulation ensure the movement of blood: first, it is sent along a large circle to the tissues and back, and then along a small one - to the lungs, where it is saturated with oxygen. Human blood circulation occurs due to the rhythmic heart work and the difference in pressure in the arteries and veins.

Circulatory organs: heart

The human circulatory system includes, in addition to arterial, venous vessels and capillaries, the heart. It is a muscular organ, hollow inside and having a conical shape. Heart located in chest cavity, is freely located in the pericardial sac, consisting of connective tissue. The bag provides constant hydration of the surface of the heart, and also supports its free contractions. The wall of the heart is formed from three layers: endocardium (inner), myocardium (middle) and epicardium (outer). The structure somewhat resembles striated muscles, but has one distinguishing feature- the ability to automatically shrink regardless of external conditions. This is the so-called automation. It is made possible by special nerve cells, which are located in the muscle and produce rhythmic excitations.

The structure of the heart

Internal is like that. It is divided into two halves, left and right, by a solid partition. Each such half has two departments - the atrium and the ventricle. They are connected by a hole equipped with a flap valve, which opens towards the ventricle. In the left half of the heart, this valve has two leaflets, and in the right half - three. Blood flows into the right atrium from the superior, inferior caval, and coronary veins of the heart, and into the left atrium from the four pulmonary veins. The right ventricle gives rise to the pulmonary trunk, which, subdivided into two branches, transports blood to the lungs. The left ventricle sends blood down the left aortic arch. At the borders of the ventricles, pulmonary trunk and aorta are semilunar valves with three leaflets on each. They close the lumens of the pulmonary trunk and aorta, and also let blood into the vessels and prevent the reverse flow of blood into the ventricles.

Three phases of the heart muscle

The alternating contraction and relaxation of the heart muscle allows blood to circulate through the two circulations. There are three phases in the work of the heart:

atrial contraction;
contraction of the ventricles (otherwise systole);
relaxation of the ventricles and atria (otherwise diastole).

The cardiac cycle is the period from one to the next atrial contraction. All cardiac activity consists of cycles, with each of them consisting of systole and diastole. The heart muscle contracts about 70-75 times in one minute (if the body is at rest), that is, about 100 thousand times in one day. At the same time, it pumps over 10 thousand liters of blood. Such a high efficiency is created by increased blood supply to the heart muscle, as well as large quantity metabolic processes in it. nervous system, in particular vegetative department regulates the functioning of the heart. Some sympathetic fibers increase contractions when irritated, while others - parasympathetic - on the contrary, weaken and slow down cardiac activity. In addition to the nervous system, the work of the heart is also regulated by the humoral system. For example, adrenaline speeds up its work, and a high content of potassium slows it down.

Pulse Concepts

The pulse is called rhythmic fluctuations in the diameter of blood vessels (arterial), which are caused by cardiac activity. The movement of blood through the arteries, including the aorta, is carried out at a speed of 500 mm / s. In thin vessels, capillaries, the blood flow slows down significantly (up to 0.5 mm / s). So low speed the movement of blood through the capillaries allows you to give all the oxygen and nutrients to the tissues, as well as take away their waste products. In veins, as they get closer to the heart, the speed of blood flow increases.

What is blood pressure?

This term means hydrodynamic in arteries, veins, capillaries. appears as a result of the implementation of its activity by the heart, which pumps blood into the vessels, and they resist. Its value in different types of vessels varies. Blood pressure increases during systole and decreases during diastole. The heart ejects a portion of blood that stretches the walls central arteries and aorta. This creates high blood pressure: the maximum systolic values are 120 mm Hg. Art., and diastolic - 70 mm Hg. Art. During diastole, the stretched walls contract, thereby pushing blood further through the arterioles and beyond. When blood moves through the capillaries, there is a gradual decrease in blood pressure to 40 mm Hg. Art. and below. When the capillaries pass into the venules, the blood pressure is only 10 mm Hg. Art. This mechanism is caused by the friction of blood particles against the walls of blood vessels, which gradually delays the flow of blood. The blood pressure continues to drop in the veins. In the hollow veins, it even becomes somewhat lower than atmospheric. This difference between the negative pressure in the vena cava and the high pressure in the pulmonary artery and aorta ensures a continuous blood circulation in a person.

Blood pressure measurement

Finding the value of blood pressure can be done in two ways. The invasive method involves the introduction of a catheter connected to a measuring system into one of the arteries (often the radial one). This method allows you to continuously measure pressure and obtain highly accurate results. A non-invasive method involves the use of mercury, semi-automatic, automatic or aneroid sphygmomanometers to measure blood pressure. Usually pressure is measured on the arm, slightly above the elbow. The resulting value shows what the value of the pressure is in this particular artery, but not in the whole body. Nevertheless, this indicator allows us to draw a conclusion about the magnitude of the blood pressure of the subject. The importance of blood circulation is enormous. Impossible without continuous blood flow normal exchange substances. Moreover, the life and functioning of the organism is impossible. Now you know how blood from the arteries enters the veins, and how the blood circulation process occurs. We hope our article was useful to you.

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This is one of the most common misconceptions.

It arose due to the consonance of words in pairs " artery - arterial" and " vein - venous» (blood) and ignorance of these terms.

Firstly, blood vessels are divided into arteries and veins depending on where they carry the blood.

Arteries are efferent vessels, and blood flows through them from the heart to the organs.

Veins are afferent vessels; they carry blood from the organs to the heart.

Secondly, arterial blood- this is not blood running through the arteries, but blood, oxygenated, a venous - saturated with carbon dioxide.

Thirdly, the conclusion from these differences is the question: “Can arterial blood flow through veins, and venous blood through arteries?” and, it would seem, a paradoxical answer to it: “Maybe!”. In the pulmonary circulation, in which the blood is saturated with oxygen in the lungs, this is exactly what happens.

Blood saturated with carbon dioxide (venous) flows from the heart to the lungs through the efferent vessels (arteries). Back - from the lungs to the heart - through the bringing vessels (veins) to the heart enters rich in oxygen blood (arterial). In a large circle that "serves" all the organs of the body and carries oxygen, arterial ("oxygen") blood runs through the arteries (from the heart), and venous ("carbon dioxide") blood runs back through the veins (to the heart).

This is the continuous movement of blood through a closed cardiovascular system, which ensures the exchange of gases in the lungs and body tissues.

The circulatory system consists of the heart and blood vessels that permeate all organs and tissues of the body.

Heart- the main organ of the circulatory system. It is a hollow muscular organ consisting of four chambers: two atria (right and left), separated by an interatrial septum, and two ventricles (right and left), separated by an interventricular septum. The right atrium communicates with the right ventricle through the tricuspid valve, and the left atrium communicates with the left ventricle through the bicuspid valve. The mass of the heart of an adult is on average about 250 g in women and about 330 g in men. The length of the heart is 10-15 cm, the transverse size is 8-11 cm and the anteroposterior is 6-8.5 cm. The volume of the heart in men is on average 700-900 cm 3, and in women - 500-600 cm 3.

The function of the heart is to rhythmically pump blood into the arteries, which comes to it through the veins. The heart contracts about 70-75 times per minute at rest (1 time per 0.8 s). More than half of this time it rests - relaxes. The continuous activity of the heart consists of cycles, each of which consists of contraction (systole) and relaxation (diastole).

There are three phases of cardiac activity:

atrial contraction - atrial systole - takes 0.1 s
ventricular contraction - ventricular systole - takes 0.3 s
total pause - diastole (simultaneous relaxation of the atria and ventricles) - takes 0.4 s

arteries- blood vessels that carry oxygenated blood from the heart to organs and tissues (only the pulmonary artery carries venous blood).

In humans, the diameter of the arteries ranges from 0.4 to 2.5 cm. The total volume of blood in the arterial system averages 950 ml. Arteries gradually branch into smaller and smaller vessels - arterioles, which pass into capillaries.

capillaries(from Latin "capillus" - hair) - the smallest vessels (the average diameter does not exceed 0.005 mm, or 5 microns), penetrating the organs and tissues of animals and humans with a closed circulatory system. They connect small arteries - arterioles with small veins - venules. Through the walls of the capillaries, consisting of endothelial cells, there is an exchange of gases and other substances between the blood and various tissues.

Vienna- blood vessels that carry blood saturated with carbon dioxide, metabolic products, hormones and other substances from tissues and organs to the heart (with the exception of pulmonary veins that carry arterial blood). The wall of the vein is much thinner and more elastic than the wall of the artery. Small and medium-sized veins are equipped with valves that prevent the reverse flow of blood in these vessels. In humans, the volume of blood in the venous system averages 3200 ml.

Circles of blood circulation

The movement of blood through the vessels was first described in 1628 by the English physician W. Harvey.

In humans and mammals, blood moves through a closed cardiovascular system, consisting of a large and small circles of blood circulation (Fig.).

The large circle starts from the left ventricle, carries blood throughout the body through the aorta, gives oxygen to the tissues in the capillaries, takes carbon dioxide, turns from arterial to venous and returns to the right atrium through the superior and inferior vena cava.

Small circle of blood circulation- pulmonary circle - serves to enrich the blood with oxygen in the lungs. It starts from the right ventricle and ends at the left atrium.

From the right ventricle of the heart, venous blood enters the pulmonary trunk (common pulmonary artery), which soon divides into two branches that carry blood to the right and left lungs.

In the lungs, arteries branch into capillaries. In the capillary networks braiding the pulmonary vesicles, the blood gives off carbon dioxide and receives a new supply of oxygen in return (pulmonary respiration). Oxygenated blood acquires a scarlet color, becomes arterial and flows from the capillaries into the veins, which, having merged into four pulmonary veins (two on each side), flow into the left atrium of the heart. In the left atrium, the small (pulmonary) circle of blood circulation ends, and the arterial blood that enters the atrium passes through the left atrioventricular opening into the left ventricle, where the systemic circulation begins. Consequently, venous blood flows in the arteries of the pulmonary circulation, and arterial blood flows in its veins.

The movement of blood through the vessels

In the left ventricle and aorta, blood pressure is higher than in the vena cava (negative pressure) and in the right atrium. The pressure difference in these areas ensures the movement of blood in the systemic circulation. High pressure in the right ventricle and pulmonary artery and low pressure in the pulmonary veins and left atrium ensure the movement of blood in the pulmonary circulation.

The highest pressure is in the aorta and large arteries (blood pressure). Arterial blood pressure is not a constant value [show]

Blood pressure- this is the blood pressure on the walls of the blood vessels and chambers of the heart, resulting from the contraction of the heart, which pumps blood into the vascular system, and the resistance of the vessels. The most important medical and physiological indicator of the state of the circulatory system is the pressure in the aorta and large arteries - blood pressure.

Arterial blood pressure is not a constant value. In healthy people at rest, the maximum, or systolic, blood pressure is distinguished - the pressure level in the arteries during the systole of the heart is about 120 mm Hg, and the minimum, or diastolic - the pressure level in the arteries during the diastole of the heart is about 80 mm Hg. Those. arterial blood pressure pulsates in time with the contractions of the heart: at the time of systole, it rises to 120-130 mm Hg. Art., and during diastole decreases to 80-90 mm Hg. Art. These pulse pressure oscillations occur simultaneously with the pulse oscillations of the arterial wall.

As blood moves through the arteries, part of the pressure energy is used to overcome the friction of the blood against the walls of the vessels, so the pressure gradually drops. A particularly significant drop in pressure occurs in the smallest arteries and capillaries - they provide the greatest resistance to the movement of blood. In the veins, blood pressure continues to gradually decrease, and in the vena cava it is atmospheric pressure or even below it. The indicators of blood circulation in different parts of the circulatory system are given in Table. one.

The speed of blood movement depends not only on the pressure difference, but also on the width of the bloodstream. Although the aorta is the widest vessel, it is the only one in the body and all the blood flows through it, which is pushed out by the left ventricle. Therefore, the maximum speed here is 500 mm/s (see Table 1). As the arteries branch out, their diameter decreases, but the total cross-sectional area of all arteries increases and the blood velocity decreases, reaching 0.5 mm/s in the capillaries. Due to such a low rate of blood flow in the capillaries, the blood has time to give oxygen and nutrients to the tissues and take their waste products.

The slowing down of blood flow in the capillaries is explained by their huge number (about 40 billion) and the large total lumen (800 times the lumen of the aorta). The movement of blood in the capillaries is carried out by changing the lumen of the supply small arteries: their expansion increases the blood flow in the capillaries, and their narrowing decreases it.

The veins on the way from the capillaries, as they approach the heart, enlarge, merge, their number and the total lumen of the bloodstream decrease, and the speed of blood movement increases compared to the capillaries. From Table. 1 also shows that 3/4 of all blood is in the veins. This is due to the fact that the thin walls of the veins can easily stretch, so they can contain much more blood than the corresponding arteries.

The main reason for the movement of blood through the veins is the pressure difference at the beginning and end of the venous system, so the movement of blood through the veins occurs in the direction of the heart. This is facilitated by the suction action of the chest ("respiratory pump") and the contraction of skeletal muscles ("muscle pump"). During inhalation, the pressure in the chest decreases. In this case, the pressure difference at the beginning and at the end of the venous system increases, and the blood through the veins is sent to the heart. Skeletal muscles, contracting, compress the veins, which also contributes to the movement of blood to the heart.

Redistribution of blood in the body

Blood circulation time

Circulation time is the time it takes for blood to travel through the entire circulation. A number of methods are used to measure blood circulation time. [show]

The principle of measuring the time of the blood circulation is that some substance that is not usually found in the body is injected into the vein, and it is determined after what period of time it appears in the vein of the same name on the other side or causes an action characteristic of it. For example, a solution of the alkaloid lobeline, which acts through the blood on the respiratory center of the medulla oblongata, is injected into the cubital vein, and the time is determined from the moment the substance is injected until the moment when a short-term breath holding or cough appears. This happens when the lobelin molecules, having made a circuit in the circulatory system, act on the respiratory center and cause a change in breathing or coughing.

In recent years, the rate of blood circulation in both circles of blood circulation (or only in a small, or only in a large circle) is determined using a radioactive isotope of sodium and an electron counter. To do this, several of these counters are placed on different parts of the body near large vessels and in the region of the heart. After the introduction of a radioactive isotope of sodium into the cubital vein, the time of appearance of radioactive radiation in the region of the heart and the studied vessels is determined.

The circulation time of the blood in humans is on average about 27 systoles of the heart. At 70-80 heartbeats per minute, a complete blood circulation occurs in about 20-23 seconds. We must not forget, however, that the speed of blood flow along the axis of the vessel is greater than that of its walls, and also that not all vascular regions have the same length. Therefore, not all blood circulates so quickly, and the time indicated above is the shortest.

Studies on dogs have shown that 1/5 of the time of a complete blood circulation occurs in the pulmonary circulation and 4/5 in the systemic circulation.

Regulation of blood circulation

Innervation of the heart. The heart, like other internal organs, is innervated by the autonomic nervous system and receives dual innervation. Sympathetic nerves approach the heart, which strengthen and accelerate its contractions. The second group of nerves - parasympathetic - acts on the heart in the opposite way: it slows down and weakens heart contractions. These nerves regulate the heart.

Innervation of blood vessels. Blood vessels are innervated by sympathetic nerves. Excitation propagating through them causes contraction of smooth muscles in the walls of blood vessels and constricts blood vessels. If you cut the sympathetic nerves going to a certain part of the body, the corresponding vessels will expand. Consequently, through the sympathetic nerves to the blood vessels, excitation is constantly supplied, which keeps these vessels in a state of some narrowing - vascular tone. When excitation increases, the frequency of nerve impulses increases and the vessels narrow more strongly - vascular tone increases. On the contrary, with a decrease in the frequency of nerve impulses due to inhibition of sympathetic neurons, vascular tone decreases and blood vessels dilate. To the vessels of some organs (skeletal muscles, salivary glands), in addition to vasoconstrictor, vasodilating nerves are also suitable. These nerves become excited and dilate the blood vessels of the organs as they work. Substances that are carried by the blood also affect the lumen of the vessels. Adrenaline constricts blood vessels. Another substance - acetylcholine - secreted by the endings of some nerves, expands them.

Regulation of the activity of the cardiovascular system. The blood supply of the organs varies depending on their needs due to the described redistribution of blood. But this redistribution can only be effective if the pressure in the arteries does not change. One of the main functions of the nervous regulation of blood circulation is to maintain a constant blood pressure. This function is carried out reflexively.

There are receptors in the wall of the aorta and carotid arteries that are more irritated if blood pressure exceeds normal levels. Excitation from these receptors goes to the vasomotor center located in the medulla oblongata and inhibits its work. From the center along the sympathetic nerves to the vessels and the heart, a weaker excitation begins to flow than before, and the blood vessels dilate, and the heart weakens its work. As a result of these changes, blood pressure decreases. And if for some reason the pressure falls below the norm, then the irritation of the receptors stops completely and the vasomotor center, without receiving inhibitory influences from the receptors, intensifies its activity: it sends more nerve impulses per second to the heart and blood vessels, the vessels constrict, the heart contracts, more often and stronger, blood pressure rises.

Hygiene of cardiac activity

The normal activity of the human body is possible only in the presence of a well-developed cardiovascular system. The rate of blood flow will determine the degree of blood supply to organs and tissues and the rate of removal of waste products. During physical work, the need of organs for oxygen increases simultaneously with the increase and increase in heart rate. Only a strong heart muscle can provide such work. To be enduring for a variety of work activities, it is important to train the heart, increase the strength of its muscles.

Physical labor, physical education develop the heart muscle. To ensure the normal function of the cardiovascular system, a person should start his day with morning exercises, especially people whose professions are not related to physical labor. To enrich the blood with oxygen, physical exercises are best done in the fresh air.

It must be remembered that excessive physical and mental stress can cause disruption of the normal functioning of the heart, its diseases. Alcohol, nicotine, drugs have a particularly harmful effect on the cardiovascular system. Alcohol and nicotine poison the heart muscle and nervous system, causing sharp disturbances in the regulation of vascular tone and heart activity. They lead to the development of severe diseases of the cardiovascular system and can cause sudden death. Young people who smoke and drink alcohol are more likely than others to develop spasms of the heart vessels, causing severe heart attacks and sometimes death.

First aid for wounds and bleeding

Injuries are often accompanied by bleeding. There are capillary, venous and arterial bleeding.

Venous bleeding is characterized by a significantly higher rate of blood flow. The escaping blood is dark in color. To stop bleeding, it is necessary to apply a tight bandage below the wound, that is, further from the heart. After stopping the bleeding, the wound is treated with a disinfectant (3% solution of hydrogen peroxide, vodka), bandaged with a sterile pressure bandage.

It should be remembered that venous, and even more arterial bleeding can lead to significant blood loss and even death. Therefore, when injured, it is necessary to stop the bleeding as soon as possible, and then take the victim to the hospital. Severe pain or fright can cause the person to lose consciousness. Loss of consciousness (fainting) is a consequence of inhibition of the vasomotor center, a drop in blood pressure and insufficient supply of blood to the brain. The unconscious person should be allowed to sniff some non-toxic substance with a strong odor (for example, ammonia), moisten his face with cold water, or lightly pat his cheeks. When olfactory or skin receptors are stimulated, excitation from them enters the brain and relieves inhibition of the vasomotor center. Blood pressure rises, the brain receives sufficient nutrition, and consciousness returns.

The heart is the fundamental organ of the body's circulatory system. Blood moves to the heart through the blood vessels (elastic tubular formations). This is the basis of nutrition of the body and its saturation with oxygen.

Composition and functional features of the heart

Heart - fibromuscular hollow organ, the uninterrupted contraction of which transports blood to cells and organs. It is located in the chest cavity, surrounded by the pericardial sac, which secretes the secret of which reduces friction during contraction. The human heart has four chambers. The cavity is divided into two ventricles and two atria.

The wall of the heart is three-layered:

epicardium - the outer layer formed from connective tissue;
myocardium - middle muscle layer;
endocarditis - a layer located inside, consists of epithelial cells.

The thickness of the muscle walls is heterogeneous: the thinnest (in the atria) are about 3 mm. The muscle layer of the right ventricle is 2.5 times thinner than the left one.

The muscular layer of the heart (myocardium) cell structure. It contains cells of the working myocardium and cells of the conducting system, which, in turn, are divided into transitional cells, P-cells and Purkinje cells. The structure of the heart muscle is similar to the structure of striated muscles, while it has the main feature, which is the automatic constant contraction of the heart with the help of impulses generated in the heart, which are not affected by external factors. This is due to the cells nervous system located in the heart muscle, in which periodic irritation occurs.

Back to ZmistuBlood "pump" of the body

Continuous blood circulation is a fundamental component of the proper metabolism between tissues and the external environment. It is important to maintain homeostasis - the ability to maintain internal balance through a series of reactions.

There are 3 stages of the heart:

Systole is the period of contraction of both ventricles so that blood is shoved into the aorta, which carries blood away from the heart. In a healthy person, 50 ml of blood is pumped in one systole.

Diastole is the relaxation of the muscle, during which there is a rush of blood. At this point, the pressure in the ventricles decreases, the semilunar valves close, and the atrioventricular valves open. The blood then enters the ventricles.

Atrial systole is the final stage in which blood completely fills the ventricles, since filling may not be completed after diastole.

Examination of the work of the heart muscle is carried out by conducting an electrocardiogram, while the curve obtained as a result of the study is recorded electrical activity hearts. Such activity is manifested when a negative charge appears on the cell surface after cellular excitation of the myocardium.

Return to zmistu Infusion of nervous and hormonal system for the functioning of the circulatory system

The nervous system has a significant impact on the work of the heart under the direct influence of internal and external factors. When the sympathetic fibers are excited, the heart rate increases significantly. If vagus fibers are involved, then heart contractions weaken.

influences humoral regulation, which is responsible for the vital processes passing through the main body fluids with the help of hormones. They leave an imprint on the work of the heart, similar to the influence of the nervous system. For example, increased content potassium in the blood has an inhibitory property, and the production of adrenaline excites.

Back to zmistuBasic and non-basic circles of blood circulation

The movement of blood throughout the body is called circulation. Blood vessels, passing one with another, form circles of blood circulation in the region of the heart: large and small. A large circle begins in the left ventricle. From the ventricle, with the contraction of the heart muscle, blood from the heart enters the aorta - the largest artery, and then spreads through the arterioles and capillaries. In turn, a small circle begins in the right ventricle. Venous blood from the right ventricle enters the pulmonary trunk, which is the largest vessel.

If necessary, additional circles of blood circulation can be allocated:

placental - oxygenated blood mixed with venous blood flowing from the mother to the fetus through the placenta and capillaries of the umbilical vein;
willisium - an arterial circle located at the base of the brain, which ensures its uninterrupted blood saturation;
cardiac - a circle extending from the aorta and carries out blood circulation in the heart.

The circulatory system has its own characteristics:

Influence of elasticity of vessel walls. It is known that the elasticity in the artery is higher than that of the veins, but the capacity of the veins is greater than that of the arteries.

The vascular system of the body is closed, while there is a huge branching of the vessels.

The viscosity of blood moving through the vessels is several times higher than the viscosity of water.

Vessel diameters range from 1.5 cm aorta to 8 μm capillaries.

Return to ZmistBlood Vessels

There are 5 types of blood vessels of the heart, which are the main organs of the entire system:

Arteries are the strongest vessels in the body that carry blood away from the heart. The walls of the artery are formed from muscle, collagen and elastic fibers. Due to this composition, the diameter of the artery can vary and adjust to the amount of blood passing through it. In this case, the arteries contain only about 15% of the volume of circulating blood.

Arterioles are smaller vessels than an artery that become capillaries.

Capillaries are the thinnest and shortest vessels. At the same time, the sum of the lengths of all capillaries in the human body is more than 100,000 km. Consist of a single layer of epithelium.

Venules are small vessels responsible for outflow in the systemic circulation with high content carbon dioxide.

Veins are medium walled vessels that carry blood to the heart, unlike arterial vessels that carry blood away from the heart. It contains more than 70% of blood.

Blood moves through the blood vessels due to the work of the heart and the difference in pressure in the vessels. Fluctuations in the diameter of blood vessels are called the pulse.

The pressure of the blood flow on the walls of the vessels and the heart is called blood pressure, which is an essential parameter of the entire circulatory system. This setting affects correct exchange substances in tissues and cells and on the formation of urine. There are several types of blood pressure:

Arterial - appears during the period of contraction of the ventricles and the release of blood flow from them.

Venous - is formed due to the energy of blood flow from the capillaries.

Capillary - directly depends on blood pressure.

Intracardiac - is formed during the period of relaxation of the myocardium.

The numerical values of blood pressure, among other things, depend on the amount and consistency of the circulating blood. The farther from the heart the measurement is taken, the lower the pressure. Moreover, the thicker the consistency of the blood, the higher the pressure.

In an adult healthy person at rest, when measuring blood pressure in the brachial artery, the maximum value should be 120 mm Hg, and the minimum should be 70-80. You should carefully monitor your blood pressure to avoid serious illness.